| Year | Value | | 2022 | 50.600256211484 | | 2021 | 50.621644811342 | | 2020 | 50.646053121593 | | 2019 | 50.676928060638 | | 2018 | 50.701295950642 | | 2017 | 50.712192555306 | | 2016 | 50.741476388193 | | 2015 | 50.795568966617 | | 2014 | 50.847212191223 | | 2013 | 50.883317424703 | | 2012 | 50.909526105348 | | 2011 | 50.875950933173 | | 2010 | 50.832040971117 | | 2009 | 50.824495679454 | | 2008 | 50.808750925202 | | 2007 | 50.787126566934 | | 2006 | 50.773893258562 | | 2005 | 50.922098819696 | | 2004 | 51.236883002439 | | 2003 | 51.568521215789 | | 2002 | 51.912336092217 | | 2001 | 52.265786642547 | | 2000 | 52.628041103517 | | 1999 | 52.84944754822 | | 1998 | 52.925157830957 | | 1997 | 53.003317187322 | | 1996 | 53.077945405727 | | 1995 | 53.14681000443 | | 1994 | 53.21056877217 | | 1993 | 53.270758662873 | | 1992 | 53.332260923952 | | 1991 | 53.401370022969 | | 1990 | 53.477486220738 | | 1989 | 53.559188986456 | | 1988 | 53.645284858009 | | 1987 | 53.735960606748 | | 1986 | 53.826231345935 | | 1985 | 53.907553457049 | | 1984 | 53.975610365076 | | 1983 | 53.929849117535 | | 1982 | 53.768982411956 | | 1981 | 53.597074564229 | | 1980 | 53.415037533078 | | 1979 | 53.226559390994 | | 1978 | 53.030379463977 | | 1977 | 52.822069356225 | | 1976 | 52.598642781387 | | 1975 | 52.357951533287 | | 1974 | 52.127283722561 | | 1973 | 52.129632828213 | | 1972 | 52.249259239386 | | 1971 | 52.225938559582 | | 1970 | 52.161585856105 | | 1969 | 52.0796125021 | | 1968 | 51.978544492586 | | 1967 | 51.859406784521 | | 1966 | 51.721747686988 | | 1965 | 51.603520321492 | | 1964 | 51.584708450205 | | 1963 | 51.605133819677 | | 1962 | 51.58130406206 | | 1961 | 51.545686926885 | | 1960 | 51.50814373792 |
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